Correcting position of undeflected spot on multigun cathode-ray tubes



- M. B. KLlNE EI'AL 1 CORRECTING POSITION 0F UNDEFLECTED SPOT 0N MULTIGUN 'CATHODE-RAY vTUBES Filed June '9 1949 Sept. 12, 1950 Fig. l

mmvroxs w m um m 30 s N W n Vfl n I Patented Sept. 12, 1950 CORRECTING POSITION OF UNDEFLECTED SPOT N MULTIGUN CATHODE-RAY TUBES Melvin B. Kline, Rutherford, and Peter S. Chris taldi, UpperMontclair, N. J., assignors to Allen B. Du Mont Laboratories, Inc., Passaic, N. J., a

" corporation offDelaware Application June 9, 1949, Serial No. 98,013

H 7 Claims. (Cl. 315-13) This invention relates to electronic circuits-tor controlling the electron beam of a cathode ray tube, particularly for correcting the undeflected spot positions of a multiple gun cathode ray tube.

In using a multiple gun cathoderay tube it is often desirable to superimpose two phenomena on the screen of the tube so that their reference; or zero axes coincide. Since the undeflected spot position on the screen is determined by the mechanical alignment of the gun structures, it requires extremely close manufacturing tolerances to insure coincidence of these spots. Maintenance of such tolerances is costly and time. con-. suming in production.

It is among the objects of this invention to provide means for electrically adjusting the spots to coincidence, thus allowing greater mechanical tolerances in the fabrication of multiple gun tubes, and to do so without changing the signal levels applied to the deflection plates.

The invention may be understood from the description and drawing inwhich:

Figure 1 is a schematic diagram of a preferred embodiment of the invention, and

Figure 2 is a schematic diagram of a modifica-- tion of the invention.

With reference to Figure l, a cathode ray tube I0 having a fluorescent screen and two electron guns H and I2, has accordingly, 'respective'sets l3 and I4 of corresponding deflection plates. A pair of output amplifier tubes 2| and 22 provide the deflection potentials for the deflection plate sets 3 and I4. These output tubes 2| and 22 arev fed by preceding stages of amplification with signals 180 out of phase with respect to each other, in the usual or well known manner. A suitable resistor is provides cathode bias potential. Aresistor 23 in series with a parallel combination of resistors 24 and 25 forms the plate load resistance for one amplifier tube 2| while the plate load for the other amlifier tube 22 comprises a resistor 26. in series with a parallel combination of resistors 27 and 28, the parallel combination being on the plate side in each instance.

One of the resistors 24 of the parallel combination connected to an amplifier tube 2| has a variable tap connected to one plate of the set I3 of deflection plates. Similarly the resistor 21 forming one of the parallel combination for the amplifier tube 22 has a variabletap 32 connected to the other plate of the set M of deflection plates, the set l3 of deflection plates-being associated with one of the electron guns I I. Likewise the other resistor 25 of the parallel combination connected to the amplifier tube 2| has a variable tap 23 connected to one of the plates of the set I4 of deflection plates, while the resistor 28 forming the other of the parallel combination connected to the amplifier tube 22 has a variable tap ,34 connected to the other plate of the set I401? deflection plates, theset M of deflection plates being associated with the second electron gun |2 within the cathode ray tube 0.; f

The taps 3| and 32 connected tothe plates of the set l3 of deflection plates are ganged mechanically to move together so that for instance,

as the tap 3| on one of the resistors 24 approaches the plate side thereof, the tap 32 on the other resistor 21 approaches the B-I- side thereof. This results in a change of the. value of 3+ voltage applied to the set l3 of deflection plates, causing the position of the spot of electron beam from the associated gun II to bechanged accordingly because-of the D. C. voltage drop on the resistors 24and 21. Thus the position of the undeflected beam spot on the screen of the tube H! is readily adjusted. At the same] time there is very little change in the A. C. component because of the fact that the taps 3| and 32 are operated over a limited range at the plate end of the load resistors for the amplifier tubes 2| and 22.

Similarly a variable tap 33 on the other parallel resistor 25 connected to amplifier tube 2|, and the variable tap 34 on the parallel resistor 28 connected to the amplifier tube 22, are connected respectively to the deflection plates forming the set I4 associated with the electron gun l2. These variable taps 33 and 34 likewise are mechanically anged to move together inv a similar manner as that described above for the variable taps 3| and 32. Again, the electron beam spot position is readily adjusted.

This arrangement makes possible a convenient adjustment of the spot positions of the two elec-' tron beams to overcome variation in the mechanical structure of the electron guns and deflection plates within the cathode ray tube. It is not necessary, therefore, to maintain closev tolerances inproduction of the tubes.

In Figure 2 there is shown a modification and arrangement whereby one set- M of deflection plates -maybe adjusted readily-with respect to the other set I3, the electron beam spot positionof the latter set being fixed. In accordance with this modification, multi-tap variable resistors areused as part of the plate load for the am' plifier tubes2| and 22=inp1ace of the parallel resistor arrangement shown" in Figure 1. One tap on each resistor is variable, the other tap on each resistor being fixed.

The position of the undeflected spot produced by the electron beam from gun II is fixed by the D. C. potential applied to the deflection plates l3 from the fixed taps 35 and 36 respectively on resistors 31 and 38. At the same time the spot produced by the electron beam from gun l2 may be adjusted in position by the variable taps 39 and 40 on the resistors 31 and 38 respectively. These variable taps 39 and 40 are connected to the deflection plates l4 and are mechanically ganged as described previously in connection with the taps shown in Figure 1.

While the invention has been specifically described and illustrated in connection with a two gun cathode ray tube, modifications will be apparent to those skilled in the art, such as for instance, adaptations for more than two electron guns in a single cathode ray tube envelope using the principles disclosed herein.

What is claimed is:

1. Apparatus for controlling the position of an electron beam spot on a cathode ray tube comprising a cathode ray tube having a flu orescent screen and a pair of electron guns producing beams of electrons directed towards said screen and a pair of deflection plate sets associated respectively with each of said guns, a pair of thermionic tubes connected respectively to said sets of deflection plates for furnishing deflection voltages therefor, each said tube having plate load resistance, taps on each said resistance connected respectively to said deflection plates, the taps connected to each plate of a set of deflection plates being mechanically ganged to vary the position of the spot on said screen produced by said electron beams.

2. Apparatus for correcting the position of an electron beam spot on a cathode ray tube comprising a cathode ray tube having a fluorescent screen, a plurality of electron guns and a plurality of sets of deflection plates associated respectively with said guns, a plurality of amplifier tubes connected respectively to said sets for supplying the deflection voltages therefor, each said amplifier tube having plate load impedance, each said impedance having a variable tap, each said ta being connected to a respective deflection plate, pairs of said taps being connected to vary simultaneously the D. C. component applied to said plates for varying the position of the spots on said screen caused by said electron beams.

3. Apparatus for correcting the position of the electron beam spot in a cathode ray tube comprising a cathode ray tube having a fluorescent screen, two electron beam guns and two sets of deflection plates associated respectively with said guns; two amplifier tubes connected respectively to said sets of plates for supplying deflection voltages thereto, each said tube having plate load resistance, each said resistance having a variable tap connected to deflection plates forming said sets, said taps being mechanically ganged thereby to vary the position of the spot on said screen caused by said beams.

4. The apparatus according to claim 3 in which said plate load resistance for each said tube comprises a pair of resistors connected in parallel each said resistor having a variable tap thereon, the tap of one of said resistors connected to one of said tubes and the tap of one of said resistors connected to the other of said tubes, being mechanically ganged and connected to one of said sets of deflection plates, the tap on the other of said resistors on one of said tubes and the tap on the other of said resistors connected to the other of said tubes, being mechanically ganged and connected to the other of said sets of deflection plates.

5. The apparatus according to claim 3 in which said plate load resistance of each of said tube comprises a multi-tap resistor one tap on each said resistor being fixed, said fixed taps being connected to one set of deflection plates, the other of said taps on each said resistor being variable and connected to the other of said sets, said variable taps being mechanically ganged.

6. Apparatus for correcting the position of an electron beam spot on a cathode ray tube comprising a cathode ray tube having a fluorescent screen and a plurality of electron guns for producing beams of electrons, deflection plates associated with each of said guns for deflecting said beams independently, an amplifier comprising a plurality of thermionic tubes connected respectively to the deflection plates associated with each said gun, and means for variably and selectively positioning a spot on said screen produced by said electron beams to a predetermined position, said means comprising a plurality of resistors connected in parallel with sliding contacts thereon forming a portion of the respective plate loads of said output tubes, said resistors being connected between the plates of said tubes and the remainder of said plate loads, said sliding contacts being directly connected to corresponding sets of said deflection plates.

7. Apparatus for correcting the position of an electron beam spot on a cathode ray tube comprising a cathode ray tube having a fluorescent screen and a plurality of electron guns for producing beams of electrons, deflection plates associated with each of saidguns for deflecting said beams independently, an amplifier comprising a plurality of thermionic tubes connected respectively to the deflection plates associated with each said gun, and means for variably and selectively positioning a spot on said screen produced by said electron beams to a predetermined position, said means comprising resistors with taps and sliding contacts thereon forming a, portion of the respective plate loads of said output tubes, said resistors being connected between the plates of said tubes and the remainder of said plate loads, said taps being directly connected to one of said sets of deflection plates associated with one of said guns and said sliding contacts being directly connected to another corresponding set of deflection plates associated with another of said guns.

MELVIN B, KLINE. PETER S. CHRISTALDI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,083,203 Schlesinger June 8, 1937 2,170,944 Glass et al. Aug. 29, 1939 2,183,634 Zworykin Dec. 19, 1939 2,227,484 Bouwers Jan. 7, 1941 2,422,100 Huff June 10, 1947 2,457,175 Parker Dec. 28, 1948 

